Casting device and associated method for lost foam casting with improved mechanical properties

ABSTRACT

The invention describes a method of casting a metal comprising the following steps: fabricating a pattern from polystyrene foam, coating the pattern with a ceramic slurry, filling sand around the pattern to create a sand mold, placing the sand mold in an open pressure vessel, filling the sand mold with a molten metal, immediately thereafter closing and pressure sealing the pressure vessel, pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time, depressurizing the sealed pressure vessel, opening the pressure vessel and removing the metal filled sand mold, and extracting the desired object from the mold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/124,014 filed Dec. 6, 2014, which hereby is incorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention is directed generally to manufacturing metal objects and more specifically to a method to lost foam cast metal objects.

BACKGROUND

Lost foam casting is a metal casting process by which a duplicate metal object is cast from a foam pattern which is destroyed in the process of making the casting. Lost foam casting, also known as expendable pattern casting, is an industrial process that allows the production of components with good surface finish and extreme intricacy in a variety of metals and high-performance alloys. The term “lost foam casting” can also refer to an object produced via the lost foam casting process. Lost foam castings are produced in specialized factories commonly referred to as foundries. Lost foam casting can produce complicated shapes that would be difficult or impossible with other methods. It is used to produce common everyday metal objects as well as large prototypes or low volume castings.

The patterns of the desired object are produced in molds or cut from solid blocks of foam. The pattern pieces, pouring basins, and the metal delivery gating system are glued together. Depending on the application, multiple patterns may be created so that they can all be cast simultaneously with the result as a pattern cluster. The foam pattern is usually coated with a ceramic wash by spraying, dipping or pouring so a uniform surface is produced. The pattern is placed inside a flask, and un-bonded sand is filled around the coated pattern. In low volume large ferrous castings, bonded sand can be packed around the pattern to form a mold, which is then removed before casting. More commonly, molten metal is then poured into the sand mold which vaporizes the foam as it fills the mold cavity. The molten metal is allowed to cool and fully solidify. Once solidified, the casting is removed by a shakeout process. The metal delivery gating system or other excess metal is trimmed away leaving the final desired object. The molding process proceeds generally along the following 7 steps:

Step #1: Fabricate a pattern from polystyrene foam.

Step #2: Assemble the foam pattern and gating system if the gating system is not already provided in the pattern tooling.

Step #3: Coat the foam pattern in a ceramic slurry of fine refractory material and allow the excess to drain off and fully dry.

Step #4: Fill non-bonded sand around the pattern to create a sand mold.

Step #5: Pour molten metal into the sand mold vaporizing the foam.

Step #6: Allow the metal to cool and fully solidify.

Step #7: Extract the casting from the sand mold, and trim the cast object.

SUMMARY OF THE INVENTION

The present invention is directed generally to manufacturing cast metal objects and more specifically to a method and device to produce expendable pattern or lost foam cast metal objects.

One embodiment of the present invention describes a method of casting a metal alloy comprising the following steps: fabricating a pattern from polystyrene foam having the appropriate geometry to generate a desired object to be cast, coating the foam pattern in a ceramic slurry of fine refractory material and allow the excess to drain off and fully dry, filling non-bonded sand around the foam pattern to create a sand mold, placing the sand mold in an open pressure vessel, filling the sand mold with a molten metal alloy, immediately thereafter closing and pressure sealing the pressure vessel, pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time said predetermined measured time sufficient for the molten metal to cool and solidify, depressurizing the sealed pressure vessel, opening the pressure vessel and removing the metal filled sand mold, and extracting the desired object from the sand mold.

Another embodiment of the present invention describes a method of casting a metal alloy comprising the following steps: fabricating a pattern from polystyrene foam having the appropriate geometry to generate a desired object to be cast, coating the foam pattern in a ceramic slurry of fine refractory material and allow the excess to drain off and fully dry, filling non-bonded sand around the foam pattern to create a sand mold, placing the sand mold in an open pressure vessel, filling the sand mold with a molten metal alloy, immediately thereafter closing and pressure sealing the pressure vessel, pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time said predetermined measured time sufficient for the molten metal to cool and solidify, withdrawing the inert gas from the sealed pressure vessel and transferring said inert gas into a reusable storage device thereby depressurizing the sealed pressure vessel, opening the pressure vessel and removing the metal filled sand mold, and extracting the desired object from the sand mold.

Another embodiment of the present invention describes a method of casting a metal alloy comprising the following steps: fabricating a pattern from polystyrene foam having the appropriate geometry to generate a desired object to be cast, coating the foam pattern in a ceramic slurry of fine refractory material and allow the excess to drain off and fully dry, filling non-bonded sand around the foam pattern to create a sand mold, filling the sand mold with a molten metal alloy, placing the sand mold in an open pressure vessel, immediately thereafter closing and pressure sealing the pressure vessel, pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time said predetermined measured time sufficient for the molten metal to cool and solidify, withdrawing the inert gas from the sealed pressure vessel and transferring said inert gas into a reusable storage device thereby depressurizing the sealed pressure vessel, opening the pressure vessel and removing the metal filled sand mold, and extracting the desired object from the sand mold.

Another embodiment of the present invention describes a device for casting a metal alloy comprising the following elements: a pressure vessel head, a pressure vessel base incorporating a surface to support a sand casting mold, a vertical travel guide in mechanical communication with the pressure vessel head and the pressure vessel base said pressure vessel head and pressure vessel base incorporating interlocking members capable of forming a pressure seal when interlocked, and an actuator capable of engaging the interlocking members thereby forming a pressure seal when the pressure vessel head is in mechanical communication with the pressure vessel base.

The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 shows a schematic representation of a pressure vessel shown in the open configuration. The pressure vessel may be comprised of a pressure vessel head, a vertical travel guide, and a pressure vessel base which is designed to form a pressure seal when in mechanical communication with the pressure vessel head.

FIG. 2 shows the pressure vessel depicted in FIG. 1 incorporating a foam-filled sand mold placed on the pressure vessel base.

FIG. 3 shows the pressure vessel depicted in FIG. 1 in the closed and unlocked, i.e. non-pressurized, configuration.

FIG. 4 shows the pressure vessel depicted in FIG. 1 in the closed and pressurized configuration while in airway communication with an external source of a pressurized inert gas.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is directed generally to manufacturing metal objects and more specifically to a device and method to lost foam or expendable pattern cast metal objects. One embodiment of the present invention is depicted schematically in FIGS. 1 through 4, highlighting the apparatus to pressurize an encased metal filled foam mold with an inert gas.

FIG. 1 depicts a pressure vessel 10 shown in the open configuration. The pressure vessel 10 may be comprised of a pressure vessel head 12, a vertical travel guide 14, and a pressure vessel base 16 which is designed to form a pressure seal when in mechanical communication with the pressure vessel head 12.

In one embodiment of the present invention, a foam pattern 20 (see FIG. 2) having the appropriate internal geometry to generate a desired object to be cast is surrounded by non-bonded sand 28 held by container 30 and may be placed on a planar substrate 18 which is part of the pressure vessel base 16. Once in place, the foam pattern 20 may be filled with a molten metal, preferably an aluminum alloy, vaporizing the foam pattern. Immediately after filling the foam pattern 20 with molten metal, the pressure vessel head 12 may be lowered and placed in mechanical communication with the pressure vessel base 16. In placing the pressure vessel head 12 in mechanical communication with the pressure vessel base 16, care may be taken to align the male interlocking elements 22A adhered to the bottom of the pressure vessel head 12 with the female counterpart interlocking elements 22B adhered to the pressure vessel base 16 as shown in FIG. 3. Once properly aligned, a linear actuator 24 attached to the pressure vessel base 16 may be energized which in turn may interlock the male and female locking elements thereby pressure sealing the pressure vessel.

Once the pressure seal has been established, an external source of an inert pressurized gas, preferably helium, may be inserted into the pressure sealed vessel by way of a valve 26 incorporated into the wall of the pressure vessel base 16 as depicted in FIG. 4. In one embodiment of the present invention the inert gas may pressurize the sealed vessel in the range of 50 to 180 pounds per square inch. The sealed, inert gas pressurized vessel may remain pressurized for a predetermined time commensurate with the size of the lost foam casting mold and the volume of molten metal encased therein.

In a preferred embodiment of the present invention, the pressure vessel and the external source of inert gas may be configured to reclaim and purify for later reuse the inert gas used previously in the process of pressurizing the pressure vessel as described above.

The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art of casting metal objects. For example, the invention anticipates other geometrical configurations for the pressure vessel including but not limited to a horizontal design in contrast to the vertical configuration outlined in the above description. Also, the present invention anticipates that the time for the molten aluminum to cool and solidify while still encased within the pressure chamber may depend upon the volume of molten aluminum poured and in many cases the ratio of volume-to-surface area of the encased aluminum, and one of ordinary skill in the art may make that determination theoretically or by experimentation. The following claims are intended to cover such modifications and devices. 

I claim:
 1. A method of casting a metal alloy comprising the following steps: fabricating a pattern from polystyrene foam having the appropriate geometry to generate a desired object to be cast; coating the pattern with a ceramic slurry; filling sand around the pattern to create a sand mold; placing the sand mold in an open pressure vessel; filling the sand mold with a molten metal alloy, thereby vaporizing the foam pattern; immediately thereafter closing and pressure sealing the pressure vessel; pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time; depressurizing the sealed pressure vessel; said predetermined measured time sufficient for the molten metal to cool and solidify; opening the pressure vessel and removing the metal filled sand mold; and extracting the desired object from the sand mold.
 2. The method of claim 1 wherein the sand based mold may be comprised of silica sand (SiO₂), chromite sand (FeCr₂O), zircon sand (ZrSiO₄), and combinations thereof.
 3. The method of claim 1 wherein the inert gas may be helium, argon, nitrogen, oxygen, or combinations thereof.
 4. The device of claim 1 wherein the sealed pressure vessel is pressurized to a value in the range of 50 to 180 pounds per square inch with the inert gas.
 5. A method of casting a metal alloy comprising the following steps: fabricating a pattern from polystyrene foam having the appropriate geometry to generate a desired object to be cast; coating the pattern with a ceramic slurry; filling sand around the pattern to create a sand mold; placing the sand mold in an open pressure vessel; filling the sand mold with a molten metal alloy, thereby vaporizing the foam pattern; immediately thereafter closing and pressure sealing the pressure vessel; pressurizing the sealed pressure vessel with an inert gas for a predetermined measured time; said predetermined measured time sufficient for the molten metal to cool and solidify; withdrawing the inert gas from the sealed pressure vessel and transferring said inert gas into a reusable storage device thereby depressurizing the sealed pressure vessel; opening the pressure vessel and removing the metal filled sand mold; and extracting the desired object from the sand mold.
 6. The method of claim 5 wherein withdrawing the inert gas from the sealed pressure vessel may include filtering and separating unwanted gaseous compounds prior to transferring the said inert gas into a reusable storage device.
 7. A device for casting a metal alloy comprising the following elements: a pressure vessel head; a pressure vessel base incorporating a surface to support an investment mold; a vertical travel guide in mechanical communication with the pressure vessel head and the pressure vessel base; said pressure vessel head and pressure vessel base incorporating interlocking members capable of forming a pressure seal when interlocked; and an actuator capable of engaging the interlocking members thereby forming a pressure seal when the pressure vessel head is in mechanical communication with the pressure vessel base.
 8. The device of claim 7 wherein the pressure vessel base incorporates a bidirectional valve device with the means to receive an inert gas from an external source and exhaust said inert gas into an external source for later reuse. 